Tire for vehicle wheels

ABSTRACT

At least one carcass ply ( 3 ) is formed by depositing a strip-like element ( 13 ) comprising longitudinal thread-like elements ( 13   a ) incorporated into a layer of elastomer material ( 13   b ), onto a toroidal support ( 11 ). Deposition of the strip-like element ( 13 ) takes place in alternated deposition sections ( 23, 24 ) each comprising two radially-extending side portions ( 23   a   , 24   a   , 23   c   , 24   c ) and a crown portion ( 23   b   , 24   b ) extending at a radially external position. The side portions of each deposition section ( 23, 24 ) are at least partly overlapped with side portions belonging to an adjacent deposition section. Associated with the carcass ply ( 3 ) are annular structures ( 4 ) comprising a circumferentially inextensible annular insert ( 32 ) axially external to an anchoring element ( 31 ). A belt structure ( 5 ), a tread band ( 8 ) and sidewalls ( 9 ) are combined with the thus formed carcass structure ( 2 ) to define a tire ( 1 ) to be submitted to a vulcanization step.

FIELD AND BACKGROUND OF THE INVENTION

[0001] The present invention relates to a tire for vehicle wheelscomprising: a carcass structure having at least one carcass ply formedof at least one thread-like element disposed along deposition paths eachextending in a substantially U-shaped conformation about the profile intransverse section of the tire, and a pair of circumferentiallyinextensible annular structures each engaged close to a respectivecircumferential inner edge of the carcass ply; a belt structure appliedto the carcass structure at a circumferentially external positionthereof; a tread band applied to the belt structure at a circumferentialexternal position thereof; at least one pair of sidewalls applied to thecarcass structure at laterally opposite positions.

[0002] Manufacture of tires for vehicle wheels involves formation of acarcass structure essentially consisting of one or more carcass pliessubstantially having a toroidal conformation and the axially oppositeside edges of which engage respective circumferentially inextensibleannular reinforcing elements called “bead cores”.

[0003] Applied to the carcass structure, at a circumferentially externalposition thereof, is a belt structure comprising one ore more beltstrips in the form of a closed ring, essentially consisting of textileor metal cords suitably oriented relative to each other and to the cordsbelonging to the underlying carcass plies.

[0004] A tread band currently consisting of a strip of elastomermaterial of appropriate thickness is applied to the belt structure, at acircumferentially external position thereof. It is to point out that, tothe aims of the present invention, by the term “elastomer material” itis intended a rubber blend in its entirety, that is the assembly made upof a base polymer suitably amalgamated with mineral fillers and/oradditives of any other type.

[0005] Finally, to the opposite sides of the tire being manufactured apair of sidewalls are applied, each of them covering a side portion ofthe tire included between a so-called shoulder region, located close tothe corresponding side edge of the tread band, and a so-called beadlocated at the corresponding bead core.

[0006] In accordance with traditional production methods, essentiallythe above listed tire components are first made separately from eachother to be then assembled during a tire-manufacturing step.

[0007] For instance, for making the carcass ply or plies to beassociated with the bead cores to form the carcass structure, productionof a rubberized fabric comprising longitudinally-disposed continuoustextile or metallic cords, through an extrusion and/or calenderingprocess, is first required. This rubberized fabric is submitted to atransverse-cutting operation to produce lengths of predetermined sizesthat are subsequently joined together so as to give rise to a continuousribbon-like semifinished product having transversely-disposed parallelcords.

[0008] Then this article of manufacture is to be cut into pieces thelength of which is correlated with the circumferential extension of thecarcass to be made.

[0009] Production methods have been recently proposed which, instead ofresorting to the production of semifinished products, make the carcassstructure directly during the tire-manufacturing step.

[0010] For example, U.S. Pat. No. 5,453,140 herein quoted as an exampleof the most pertinent state of the art, discloses a method and anapparatus according to which the carcass structure is formed by layingdown a single continuous thread according to alternating depositionpaths placed consecutively in side by side relationship in acircumferential direction, onto a toroidal support having a shapecorresponding to the inner shape of the tire to be made.

[0011] In more detail, the toroidal support is previously coated with araw-rubber layer having a dual function, i.e. that of convenientlyadhering to the deposited thread so as to hold the individual depositionsections thereof at a fixed positioning, and that of forming anair-proof inner liner in the finished tire.

[0012] The individual thread, directly drawn from a reel, is engaged bysliding members leading it to a movable guide member operating at thetoroidal support. The movable guide member moves in a sliding path oftravel having an advance section and a return section mutuallyinterconnected to form an endless line lying in a plane radial to thetoroidal support. Each of the advance and return sections extends in asubstantially C-shaped configuration around the profile in transversesection of the toroidal support.

[0013] In this way, each time the guide element covers one of theadvance or return sections of the sliding path of travel, deposition ofthe thread onto the toroidal support is caused, thereby forming adeposition section extending in a U-shaped conformation around theprofile in transverse section of the toroidal support itself. At theinstant intervening between formation of a deposition section andformation of the subsequent deposition section, the toroidal support isrotated through a predetermined angular pitch, making the apparatusready for formation of a new deposition section disposedcircumferentially in side by side relationship with the previouslydeposited section.

[0014] Pick-up devices making use of fork-shaped elements engage thethread at the end region of the just-formed deposition section, toprevent dragging along of the latter by the guide member during theinitial formation step of the subsequent deposition section. Retentiondevices making use of presser elements conveniently act at thetransition region between two deposition sections in succession to causethe end flaps thereof to adhere to the side surface of the toroidalsupport.

[0015] Tires obtained by this production method have a carcass structurein which the cords forming the carcass ply or plies consist of a singlethread-like element forming a plurality of consecutive sectionstransverse to the tire, disposed parallelly in side-by-side relationshipin a circumferential direction and deposited in respectively oppositedirections so as to define an alternated course.

[0016] Within the scope of the carcass structure manufacture, as can belearnt from Patents EP 0 664 231 and EP 0 664 232, the depositionsections formed by the individual thread-like element are also providedto be placed in an alternated sequence at axially opposite positionsrelative to one or more annular anchoring elements constituting saidbead cores.

[0017] In accordance with the present invention, different advantageshave been found to be achieved if the carcass ply or plies are made bydepositing at least one strip-like element essentially comprising alayer of raw elastomer material incorporating two or more parallelthread-like elements disposed longitudinally, in alternated consecutivesections transverse to the tire.

SUMMARY OF THE INVENTION

[0018] In more detail, the invention relates to a tire for vehiclewheels, wherein at least one carcass ply comprises: at least onecontinuous strip-like element comprising a plurality of longitudinal andparallel thread-like elements at least partly coated with at least onelayer of raw elastomer material; said strip-like element having distinctdeposition sections each of which extends according to a substantiallyU-shaped conformation about the profile in transverse section of thetire, to define two side portions substantially extending in planesorthogonal to a geometric axis of rotation of the tire at mutuallyspaced apart positions in an axial direction, and a crown portionextending in a radially external position between the side portions, thecrown portions of each deposition section being disposed in side by siderelationship along the circumferential extension of the tire, whereasthe side portions of each deposition section are each partly overlappedwith a side portion of at least one adjacent deposition section.

[0019] In more detail, the side portions in mutual-overlappingrelationship mutually converge at the geometric axis of rotation of thetire.

[0020] Advantageously, mutual overlapping of the side portions of thedeposition sections progressively decreases starting from a maximumvalue at the radially inner ends of the side portions until a zero valueat transition regions between said side portions and crown portions.

[0021] Preferably, the side portions in mutual-overlapping relationshipare joined to each other at a bending end region wherein the strip-likeelement is folded upon itself.

[0022] In a preferential solution the individual deposition sections aredisposed according to a circumferential distribution pitch correspondingto the width of the strip-like element.

[0023] In accordance with a possible alternative solution, theindividual deposition sections are disposed according to acircumferential distribution pitch corresponding to a multiple of thewidth of the strip-like element.

[0024] Preferably, the strip-like element has a width corresponding to asubmultiple of the circumferential tire extension, as measured at itsequatorial plane.

[0025] According to a further aspect of the invention, the side portionsof the deposition sections have regions of enlarged width close to theinner circumferential edges of the carcass structure.

[0026] The thread-like elements comprised within the strip-like elementare mutually moved apart at said regions of enlarged width.

[0027] In a preferential embodiment, the strip-like element has a widthincluded between 3 mm and 15 mm, and preferably comprises three to tenthread-like elements.

[0028] Each of said thread-like elements may be advantageously made upof a textile cord of a diameter included between 0.6 mm and 1.2 mm, or ametallic cord of a diameter included between 0.3 mm and 2.1 mm.

[0029] Preferably, the thread-like elements are disposed within thestrip-like element according to a mutual distance between centers notlower than 1.5 times the diameter of the thread-like elements, and adensity of at least six thread-like elements per centimeter,circumferentially measured on the carcass structure at the medianequatorial plane of the tire.

[0030] Advantageously, the side portions of the deposition sections haveend flaps corresponding to the inner circumferential edges of thecarcass ply turned back about the respective inextensible annularstructures.

[0031] In accordance with a further innovatory aspect of the invention,that can be also advantageously adopted independently of the abovelisted innovatory features, each of said inextensible annular structurescomprises: an annular anchoring element disposed coaxially with saidtire; a circumferentially inextensible annular insert disposed axiallyin side by side relationship with the annular anchoring element andsubstantially extending parallelly to adjacent surfaces of the carcassply, said annular insert being formed of at least one thread-likeelement extending in concentric coils; a filling body of elastomermaterial intimately joined to the annular anchoring element and thecircumferentially inextensible annular insert.

[0032] In more detail, the circumferentially inextensible annular insertcan be disposed axially in side by side relationship with the annularanchoring element either at an axially outer position or at an axiallyinner position relative to an equatorial plane of the tire.

[0033] Preferably said circumferentially inextensible annular insert hasa radial extension substantially corresponding to at least twice theradial extension of the bead core or in any case greater than thelatter.

[0034] According to a possible embodiment, the carcass structure furthercomprises at least one second carcass ply similar in structure to thefirst carcass ply. In other words, the possible second carcass plyadvantageously comprises at least one continuous strip-like elementcomprising a plurality of longitudinal and parallel thread-like elementsat least partly coated with at least one layer of raw elastomermaterial, said strip-like element have alternating deposition sectionseach of which extends in a substantially U-shaped conformation about theprofile in transverse section of the tire, to define two side portionssubstantially extending in planes orthogonal to a geometric axis ofrotation of the tire at mutually spaced apart positions in an axialdirection, and a crown portion extending at a radially external positionbetween the side portions, the crown portions of each deposition sectionbeing disposed consecutively in side by side relationship along thecircumferential extension of the tire, whereas the side portions of eachdeposition section are each partly overlapped with one side portion ofat least one consecutive deposition section.

[0035] In accordance with a further preferential aspect of theinvention, to be exploited independently of the above statements too,the belt structure comprises: at least one first continuous belt stripformed of a plurality of belt lengths each comprising at least one layerof raw elastomer material at least partly incorporating a plurality ofparallel cords disposed transversely, said belt lengths being disposedconsecutively in circumferential alignment on the tire and in mutualside by side relationship along respective junction edges parallel tosaid cords.

[0036] Each of said belt lengths preferably has a circumferential sizecorresponding to a submultiple of the circumferential extension of thebelt strip.

[0037] The belt structure may further comprise at least one second beltstrip formed of at least one continuous elongated element wound in coilsdisposed axially in side by side relationship and extendingcircumferentially about the first belt strip.

[0038] These winding coils can be disposed mutually in side by siderelationship according to a varying axial-distribution pitch, forinstance greater close to the median equatorial plane of the tire thanat the opposite side edges of the belt structure.

[0039] The tread band may advantageously comprise at least onecontinuous sheet of raw elastomer material circumferentially wound aboutthe belt structure in a plurality of radially superposed coils.

[0040] Preferably, said continuous sheet of elastomer material has aprogressively decreasing width away from the rotation axis of the tire.

[0041] In accordance with a further independent aspect of the invention,each of said sidewalls preferably comprises a radially outer portion anda radially inner portion made of a first and a second elastomer materialrespectively and intimately joined to each other by an overmoldingprocess.

[0042] The carcass structure may also be comprised of at least onesealing layer made of elastomer material impervious to air, coating saidcarcass ply internally of the tire.

[0043] Said air-tight layer or “liner” is preferably made up of at leastone ribbon-like band of an air-proof elastomer material extending incoils disposed side by side along the profile in transverse section ofthe tire.

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Further features and advantages will be best understood from thedetailed description of a preferred but non-exclusive embodiment of atire for vehicle wheels according to the present invention. Thisdescription will be given hereinafter with reference to the accompanyingdrawings, given by way of non-limiting example, in which:

[0045]FIG. 1 is a fragmentary perspective view in split of a tireobtained in accordance with the present invention;

[0046]FIGS. 2 and 3 diagrammatically show an apparatus for making thecarcass ply, in different operating steps respectively, seen in adirection orthogonal to a diametrical section plane of a toroidalsupport carrying the tire during the manufacturing step;

[0047]FIG. 4 is a diagram showing the manufacture of a strip-likeelement intended for forming the carcass ply or plies;

[0048]FIG. 5 shows an embodiment of said strip-like element intransverse section;

[0049]FIG. 6 is a fragmentary perspective view diagrammatically showingthe deposition sequence of a strip-like element for the purpose offorming a carcass ply of the tire in accordance with the invention;

[0050]FIG. 7 is a fragmentary diametrical section view of aninextensible annular structure to be inserted at the tire bead, during amolding step for manufacturing the tire;

[0051]FIG. 8 is a fragmentary perspective view of an inextensibleannular structure laterally applied to the carcass ply;

[0052]FIG. 9 is a diagram showing accomplishment of a continuous ribbonand cutting of same into lengths of predetermined shape and sizes formaking a first belt strip;

[0053]FIG. 10 is a transverse section view of said continuous beltribbon;

[0054]FIG. 11 is a fragmentary perspective view showing deposition ofthe ribbon lengths in a circumferential alignment onto the carcassstructure for formation of said first belt strip;

[0055]FIG. 12 is a diagram referring to production of a rubberizedelongated element intended for making a second belt strip;

[0056]FIG. 13 is a fragmentary perspective view in section showing thestep of forming said second belt strip by the continuous elongatedelement;

[0057]FIG. 14 is a diagram showing formation of a continuous elastomersheet intended for making a tread band;

[0058]FIG. 15 is a fragmentary perspective view in section showing thetread band made by winding the continuous sheet in several superposedcoils;

[0059]FIG. 16 diagrammatically shows formation of the tire sidewalls intransverse section;

[0060]FIG. 17 is a fragmentary perspective view showing application ofthe sidewalls to the tire during its manufacturing step;

[0061]FIG. 18 is a fragmentary perspective view in section showing thetire in reference provided with an inextensible annular structure madein accordance with a possible alternative embodiment of the invention;

[0062]FIG. 19 is a transverse half-section showing a tire in accordancewith the invention mounted on a respective rim and in a condition ofslip run.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0063] With reference to the cited drawings and in particular to FIGS. 1and 17, a tire for vehicle wheels in accordance with the presentinvention has been generally identified by reference numeral 1.

[0064] Tire 1 essentially comprises a carcass structure 2 having atleast one carcass ply 3 substantially of a toroidal conformation andengaged, by its opposite circumferential edges, with a pair ofinextensible annular structures 4 that, when the tire is completed, arelocated in the region usually identified as “bead”.

[0065] Applied to the carcass structure 2, at a circumferentially outerposition, is a belt structure 5 comprising one or more belt strips 6, 7.A tread band 8 is circumferentially superposed on the belt structure 5and longitudinal and transverse cuts 8 a are formed in said tread band8, following a molding operation carried out concurrently with the tirevulcanization, and such disposed as to define a desired “tread pattern”.

[0066] The tire also comprises a pair of so-called “sidewalls” 9 appliedlaterally to opposite sides of the carcass structure 2.

[0067] The carcass structure 2 may possibly be coated, on its innerwalls, with an air-proof elastomer-material layer 10, i.e. a so-called“liner”, essentially consisting of a layer of elastomer materialimpervious to air, adapted to ensure the hermetic seal of the inflatedtire.

[0068] Assembling of the above listed components, as well as productionof one or more of said components, takes place with the aid of atoroidal support 11, diagrammatically shown in FIGS. 2 and 3, having thesame configuration as the inner walls of the tire to be manufactured.

[0069] In a preferential solution the toroidal support 11 has reducedsizes relative to those of the finished tire, according to a linearamount preferably included between 2% and 5%, measured, just as anindication, along the circumferential extension of the support itself atan equatorial plane X-X thereof which is coincident with the equatorialplane of the tire itself.

[0070] The toroidal support 11, which is not described or illustrated indetail in that it is not particularly of importance to the purposes ofthe invention, may for example consist of a collapsible drum or aninflatable chamber or bladder suitably reinforced so that it may takeand maintain the desired toroidal conformation under inflationconditions.

[0071] After taking into account the above statements, manufacture oftire 1 first involves formation of the carcass structure 2 starting withpossible formation of the air-proof layer or liner 10.

[0072] This liner 10 can be advantageously made by circumferentiallywinding about the toroidal support 11, at least one ribbon-like band 12of air-proof elastomer material, produced from an extruder and/or acalender located close to the toroidal support itself. As viewed fromFIG. 1, winding of the ribbon-like band 12 substantially takes place incircumferential coils disposed consecutively in side by siderelationship to follow the profile in transverse section of the outersurface of the toroidal support 11.

[0073] For descriptive purposes, by “profile in transverse section” itis herein intended a configuration exhibited by the half-section of thetoroidal support 11 sectioned along a plane radial to a geometricrotation axis thereof, not shown in the drawings, which is coincidentwith the geometric axis of rotation of the tire being manufactured.

[0074] Concurrently with winding of the ribbon-like band 12, applicationof a pair of auxiliary annular elements 12 a can be carried out close tothe inner circumferential edges of the carcass structure during itsmanufacturing step. Each of these auxiliary annular elements 12 a can beobtained for example by winding the ribbon-like band 12 in a coildisposed axially side by side with the corresponding coil located at theinner perimetric edge of liner 10 defined or to be defined on thetoroidal support 11. Alternatively, the auxiliary annular elements 12 acan be made up of at least one auxiliary ribbon-like band obtained froma respective extruder located at the toroidal support 11.

[0075] In accordance with the present invention, the carcass ply 3 isdirectly formed on the toroidal support 11 by depositing thereon,following alternating paths, at least one strip-like element 13preferably having a width included between 3 mm and 15 mm, as betterclarified in the following.

[0076] As shown in FIG. 4, preparation of the strip-like element 13essentially involves that two or more thread-like elements 13 a, andpreferably three to ten thread-like elements 13 a, fed from respectivereels 14, should be guided through a first extruder 15 associated with afirst extrusion apparatus 16 carrying out feeding of raw elastomermaterial through the extruder itself.

[0077] It is pointed out that, in the present description by “extruder”it is intended that part of the extrusion apparatus also identified inthis particular field by the term “extrusion head”, provided with aso-called “die” passed through by the product being worked at an outletport shaped and sized according to the geometrical and dimensionalfeatures to be given to the product itself.

[0078] The elastomer material and thread-like elements 13 a areintimately joined together within the extruder 15, thereby generatingthe continuous strip-like element 13 at the outlet thereof, whichelement is formed of at least one layer of elastomer material 13 b inthe thickness of which the thread-like elements themselves areincorporated.

[0079] Depending on requirements, it is possible to guide thethread-like elements 13 a in the extruder 15 in such a manner that theyare not integrally incorporated into the layer of elastomer material 13b but appear on one or both surfaces thereof.

[0080] The thread-like elements 13 a may each consist for example of atextile cord preferably having a diameter included between 0.6 mm and1.2 mm, or a metallic cord preferably having a diameter included between0.3 mm and 2.1 mm.

[0081] Advantageously, if required, the thread-like elements 13 a can bedisposed in the strip-like element 13 in such a manner that they givethe carcass ply 3 thus obtained unexpected qualities of compactness andhomogeneity. For the purpose, the thread-like elements 13 a can be forexample disposed according to a density greater than six thread-likeelements/centimeter, measured circumferentially on the carcass ply 3close to the equatorial plane X-X of tire 1. In any case it ispreferably provided that the thread-like elements 13 a should bedisposed in the strip-like element 13 according to a mutual distancebetween centers not lower than 1.5 times the diameter of the thread-likeelements themselves, in order to enable an appropriate rubberizingoperation between the adjacent threads.

[0082] The continuous strip-like element 13 coming out of extruder 15can be advantageously guided, optionally through a firstaccumulator-compensator device 17, on a deposition apparatus 18diagrammatically shown in FIGS. 2 and 3.

[0083] The deposition apparatus 18 essentially comprises first guidemembers 19, consisting for example of a pair of rollers borne onstationary rotation axes, arranged to engage the continuous strip-likeelement 13 produced by the extruder 15. Downstream of the first guidemembers 19, the strip-like element 13 comes into engagement with secondguide members 20 consisting of further rollers for example, mounted on acarriage 21 reciprocating in a direction oriented transversely to theequatorial plane X-X of the toroidal support 11. Slidably linked to themovable carriage 21, in a direction substantially perpendicular to themovement direction of the carriage itself, is at least one distributorelement 22 consisting of a further roller, for example.

[0084] Components intended for mutual connection and movement of thedistributor element 22 and movable carriage 21 are not shown in theaccompanying drawings in that they can be made in any manner convenientto a person skilled in the art, and in any case they are not ofimportance to the aims of the present invention.

[0085] By a combination between the transverse movement of carriage 21and radial movement of the distributor element 22, the distributorelement lends itself to be translated by a reciprocating motion along atrajectory “t” extending according to a substantially U-shapedconformation about the profile in transverse section of the toroidalsupport 11.

[0086] The toroidal support 11 can be driven in angular rotation in astep-by-step movement in synchronism with the movement of thedistributor element 22, in such a manner that the strip-like element 13is deposited onto the toroidal support in consecutive depositionsections 23, 24, transverse to the tire, disposed parallelly inside-by-side relationship in a circumferential direction and accordingto respectively opposite directions, so as to define an alternatingcourse.

[0087] In more detail, each of the deposition sections 23, 24 extends ina U-shaped conformation about the profile in transverse section of thetoroidal support 11, to define two side portions 23 a, 23 c, 24 a, 24 csubstantially extending in planes orthogonal to the geometric axis ofrotation of the toroidal support, at mutually spaced apart positions inan axial direction, and a crown portion 23 b, 24 b extending at aradially outer position relative to the side portions 23 a, 23 c, 24 a,24 c.

[0088] For convenience in description, the deposition sections obtainedas a result of a translation from right to left of the deposition member22 with reference to FIGS. 2 and 3, will be hereinafter referred to asfirst deposition sections 23. Those obtained from translation of thedistributor element in the opposite direction will be, instead,identified as second deposition sections 24.

[0089] In more detail, the deposition sequence of the strip-like element13 on the toroidal support 11 is the following.

[0090] Starting is assumed to take place from an initial situation inwhich, as shown in FIG. 2, the distributor element 22 is located in itslefthand end-of-stroke position of its movement trajectory “t”. Startingfrom this position, the distributor element 22 is substantiallytranslated radially away from the geometric axis of rotation of thetoroidal support 11, to form a first side portion 23 a of the firstdeposition section 23.

[0091] Due to the sticky character of the raw elastomer material forminglayer 13 b coating the thread-like elements 13 a, a steady adhesion ofthe strip-like element 13 on the surfaces of the toroidal support 11 isensured, even in the absence of liner 10 on the toroidal support itself.In the case that, as diagrammatically shown in FIGS. 2 and 3, thetoroidal support 11 has side portions 11 a of a concave profile, locatedin the regions corresponding to the sidewalls of the tire beingproduced, the above described adhesion takes place as soon as thestrip-like element 13 comes into contact with the toroidal supportitself at a radially external region of its profile in transversesection.

[0092] In addition to or in place of the above described exploitation ofthe natural sticky character of the elastomer material, retention of thestrip-like element 13 on the toroidal support 11 can be obtained bycarrying out a suction action produced through one or more appropriateholes 28 arranged on the toroidal support.

[0093] In the initial step of the distributor-element stroke 22 awayfrom the geometric axis of rotation of the toroidal support 11, thestrip-like element 13 is folded upon itself forming a bending region 25representing a transition between the first side portion 23 a of thedeposition section 23 which is about to be formed and a second sideportion 24 b belonging to a previously formed deposition section 24.During formation of the first side portion 23 a, the strip-like element13 is conveniently retained at said bending region 25, by a retentionelement 26 (FIG. 3) engaging in the bending region in a manner betterdescribed in the following.

[0094] Concurrently with formation of the first side portion 23 a, thetoroidal support 11 is rotated about its own geometric axis of rotationrelative to the distributor element 22, according to an angular pitchcorresponding to half the circumferential distribution pitch of thedeposition sections 23, 24. Consequently, the first side portion beingformed will take a correspondingly inclined orientation relative to thedirection of movement performed by the distributor element 22 away fromthe geometric axis of rotation of the support itself.

[0095] In the embodiment diagrammatically shown in FIG. 2, where thecircumferential distribution pitch of the individual deposition sections23, 24 corresponds to the width of the strip-like element 13, theangular-rotation pitch of the toroidal support 11 will correspond tohalf the width of the strip-like element itself.

[0096] In any case, the circumferential distribution pitch of thedeposition sections 23, 24 may be provided to correspond to a multipleof the width of the strip-like element 13. In this case, theangular-movement pitch of the toroidal support 11 will in any casecorrespond to half said circumferential distribution pitch. It is topoint out that, to the aims of the present invention, when it is nototherwise stated, the term “circumferential” refers to a circumferencelying in the equatorial plane X-X and close to the outer surface of thetoroidal support 11.

[0097] When the support element 22 comes close to the top of its strokeaway from the geometric axis of rotation of the toroidal support 11, themovable carriage 22 is translated in its movement direction from left toright with reference to FIG. 2. Under this circumstance, the distributorelement 22 moves in a direction substantially parallel to the geometricaxis of rotation of the toroidal support 11 in such a manner that, in aposition radially external to the latter, there is formation of a crownportion 23 b of the deposition section 23 being made.

[0098] When carriage 21 has substantially completed its translationstroke, the distributor element 22 is moved substantially radially closeto the geometric rotation axis of the toroidal support 11. Under thiscircumstance a second side portion 23 c of the first deposition section23 is formed.

[0099] Concurrently with formation of this second side portion 23 c, thetoroidal support 11 is rotated relative to the distributor element 22 atan angular pitch identical with the one previously performed.

[0100] When the distributor element 22 is about to complete its strokeof moving close to the geometric rotation axis of the toroidal support11, a further retention element (not shown) identical with thepreviously mentioned retention element 26 and in mirror imagerelationship therewith is disposed alongside the second side portion 23b which has been just formed, in the same manner as shown in chain linein FIG. 3 in connection with the retention element 26 located on thelaterally opposite side.

[0101] Preferably, the retention element 26 is then laterally movedclose to the toroidal support 11, to enable passage of the distributorelement 22 during its upward movement, as a result of which,concurrently with formation of a first side portion 24 a of a new seconddeposition section 24, the strip-like element 13 will be turned backabout the retention element thereby forming a new bending region 25.

[0102] Simultaneously with formation of the first side portion 24 a ofthe second deposition section 24, the toroidal support 11 performs a newangular-rotation step that, being added to the angular step performedduring deposition of the second side portion 23 b of the firstdeposition section 23, makes the distributor element 22 ready to formthe crown portion 24 b of the second deposition section 24 at a positionspaced apart from the previously formed deposition section 23 accordingto the desired circumferential distribution pitch.

[0103] The retention element 26 is axially disengaged from the bendingregion 25 after formation of the crown portion 24 b has begun. Actually,in this step the assurance exists that the strip-like element 13 hascome into contact with the surface of the toroidal support 11 at a pointdownstream of the just-formed first side portion 24 a, and that it isnot liable to carry out undesired displacements that could impair thedeposition geometry of the strip-like element.

[0104] Once the retention element 26 has been drawn out of the bendingregion 25, the side portions 23 c, 24 c of the deposition sections 23,24 can be submitted to a pressing step against the side walls of thetoroidal support 11. For the purpose, a pair of presser rollers 27 orequivalent means may be provided, and they operate on opposite sides ofthe toroidal support 11 and are each arranged so as to repeatedlyoperate on the first and second side portions belonging to twocontiguous deposition sections.

[0105] Only one of these presser rollers 27 has been diagrammaticallyshown in FIG. 3.

[0106] The above described operating sequence of the depositionapparatus 18 enables the crown portions 23 b, 24 b of each depositionsection 23, 24 in the obtained carcass ply 3 to be disposedconsecutively in side by side relationship along the circumferentialextension of the toroidal support 11, whereas the side portions 23 a, 23c, 24 a, 24 c of each deposition section 23, 24 are each disposed insuperposition relationship with a side portion of at least oneconsecutive deposition section.

[0107] More specifically, the first side portion 23 a, 24 a of eachdeposition section 23, 24 is partly superposed on the second sideportion 23 c, 24 c of the previously formed deposition section 23, 24.

[0108] As clearly shown in FIG. 6, the side portions 23 a, 24 c inmutual superposition relationship move towards each other substantiallyin the direction of the geometric axis of rotation of the toroidalsupport 11, according to an angle 6 the value of which is correlatedwith the width “L” of the strip-like element 23, 24, and in any casewith the circumferential distribution pitch of the deposition sections23, 24, as well as the difference between a maximum radius R′ and aminimum radius R to be measured at a point of maximum distance and apoint of minimum distance respectively from the geometric axis ofrotation of the toroidal support 11.

[0109] Due to the mutual convergence between the first and secondcontiguous side portions 23 a, 24 c and 24 a, 23 c, mutual superpositionof the same is progressively decreasing starting from a maximum value atthe radially inner ends of the side portions, where said portionsmutually meet at the bending region 25, until a zero value at thetransition region between the side portions and crown portions 23 b, 24b.

[0110] It is to note that, due to the difference between the minimum andmaximum radii R and R′, the average density of the thread-like elements13 a, i.e. the amount of the thread-like elements present in acircumferential section of given length, would have a tendency toprogressively increase on moving close to the geometric rotation axis ofthe toroidal support 11.

[0111] Actually, this increase in density is proportional to the ratiovalue between the maximum radius R′ and minimum radius R.

[0112] However, in the tire made in accordance with the presentinvention, mutual superposition of side portions 23 a, 24 c and 24 a, 23c actually gives rise to halving of the average density to be measuredalong the inner circumferential edges of the obtained carcass ply 3,i.e. at the bending regions 25.

[0113] Under this circumstance, the bending portions 25 would bemutually joined in the circumferential direction, giving rise to ahomogeneous distribution of the thread-like elements 13 a along theinner circumferential edges of the carcass ply 3, only if ratio betweenthe maximum diameter R′ and minimum diameter R corresponds to 2.

[0114] When, on the contrary, as it usually occurs, the ratio valuebetween the maximum radius R′ and minimum radius R is less than 2, thebending portions 25 would tend to arrange themselves according to acircumferential distribution pitch greater than the width of thestrip-like element 13, thus giving rise to empty spaces between onebending region 25 and another one.

[0115] If the presence of these empty spaces is wished to be avoided, soas to consequently obtain a maximum structural homogeneity of thecarcass ply 3 close to the inner circumferential edges of the carcassply 3, a pressing step is provided to be sequentially executed on thestrip-like element 13 at the regions of its longitudinal extensioncorresponding to the side portions 23 a, 23 c, 24 a, 24 c, so as todefine regions of increased width 1′ on the extension of the strip-likeelement, which regions are located at the inner circumferential edges ofthe formed carcass ply 3.

[0116] Said pressing action can be carried out by a presser roller 29mounted on the movable carriage 21 for example, and adapted to beselectively set in motion by an actuator 30 to press the strip-likeelement 13 against one of the rollers being part of the secondtransportation unit 20.

[0117] Actuator 30 is sequentially activated during deposition of thestrip-like element 13, so as to cause crushing of same at the sectionsof longitudinal extension intended to form the side portions 23 a, 23 c,24 a, 24 c. Thrust exerted by actuator 30 can be convenientlyestablished in order to obtain an increasingly growing crushing actionfor example on moving close to the bending regions 25 and aprogressively decreasing action on moving away therefrom. The crushingaction causes a reduction in the thickness of the elastomeric layer 13 band an increase in the width of the strip-like element 13 which, as aresult, will cause the thread-like elements 13 a to move apart from eachother.

[0118] By conveniently measuring the thrust action exerted by theactuator, width of the strip-like element 13 can be increased until anamount L′ involving mating of each bending region 25 with the adjacentbending regions.

[0119] By suitably inclining the orientation of the geometric axis ofrotation of the toroidal support 11 relative to the movement directionof the movable carriage 21, the crown portions 23 b, 24 b of thedeposition sections 23, 24 can be given a desired inclination,preferably included between 0° and 15° and more preferably of 3°,relative to a radial plane passing by the geometrical axis. It is alsoto note that, due to the rotation steps carried out by the toroidalsupport 11 concurrently with the formation of each deposition section23, 24, the side portions 23 a, 23 c, 24 a, 24 c of the depositionsection will be inclined at an angle of δ/2 relative to a radial planecrossing the side portions themselves, the first side portions 23 a, 24a having an opposite inclination direction with respect to the secondside portions 23 c, 24 c.

[0120] Accomplishment of a carcass structure 2 generally comprises thestep of applying said inextensible annular structure 4 to an area closeto each of the inner circumferential edges of the carcass ply 3 obtainedin the previously described manner, for the purpose of creating thecarcass regions, known as “beads”, which are specifically intended forensuring anchoring of the tire to a corresponding mounting rim; inaccordance with a preferred embodiment of the tire, the carcass plythereof is obtained in the above described manner.

[0121] Each of these inextensible annular structures 4 (FIG. 7)comprises an annular anchoring element 31, of the type usually called“bead core”, which can be made up, for example, of one or more metallicwires twisted together or wound in side-by-side coils to define aprofile of substantially circular or quadrangular transverse section.

[0122] In accordance with a preferred embodiment, to be alsoadvantageously associated with the present invention, acircumferentially inextensible annular insert 32 is combined with thebead core 31 and it approximately extends in a plane parallel to theadjacent surfaces of the carcass ply 3 along a radial extensiondetermined by the difference between the minimum inner radius and themaximum outer radius of the annular insert, preferably equal to at leasttwice the radial extension of the bead core 31 or in any case greaterthan the latter.

[0123] In a first embodiment shown in FIGS. 1, 8, 15, 17 and 19, theinextensible annular insert 32 is located at an axially outer positionrelative to the bead core 31. In other words, the annular insert 32 islocated, with respect to the bead core 31, at a laterally oppositeposition relative to the equatorial plane X-X.

[0124] In a possible alternative solution, shown in FIG. 18, theinextensible annular insert 32 is, on the contrary, located at anaxially inner position relative to the bead core 31, i.e. on the sidefacing the equatorial plane X-X. In this case, the annular insert 32preferably substantially extends in contact with the adjacent carcassply 3.

[0125] The annular insert 32 is made up of at least one metallic wirewound up to form several substantially concentric coils 32 a. Coils 32 acan be defined by a continuous spiral or by concentric rings formed ofrespective metallic wires.

[0126] Advantageously, during the tire use, the inextensible annularinsert 32 is adapted to efficiently counteract the bead tendency torotate about the profile in transverse section of the bead core 31,under the effect of slip thrusts directed parallelly to the rotationaxis of tire 1. This tendency to rotation is particularly apparent whenthe tire is employed under conditions of partial or total deflation.

[0127] Preferably, for accomplishment of each annular structure 4, firstthe inextensible annular insert 32 is formed within a molding cavity 34defined in a mold 34 a, 34 b, by deposition of at least one thread-likeelement in concentric coils 32 a disposed in mutual side by siderelationship, according to circumferences of increasingly growingdiameter about their geometric winding axis corresponding to therotation axis of the tire.

[0128] This operation can be advantageously performed by winding thethread-like element in a helical seating arranged in a first cheek 34 aof mold 34 a, 34 b which for the purpose can be driven in rotation aboutits own geometric axis.

[0129] The deposition step of the thread-like element can beadvantageously preceded by a rubberizing step in which the thread-likeelement, preferably of metallic material, is coated with at least onelayer of raw elastomeric material that, in addition to ensuring anexcellent rubber-metal bond on the thread-like element itself, promotesadhesion thereof for a steady placement in the above mentioned helicalseating.

[0130] The first cheek 34 a may be also advantageously provided to bemade of a magnetic material, or to be activated in an electromagneticmanner so as to attract and retain the thread-like element againstitself, thereby ensuring a steady positioning of the coils 32 a formedby it.

[0131] The bead core 31 is then located within the molding cavity 34 andafterwards closure of the molding cavity 34 is carried out by moving thefirst cheek 34 a close to a second matching cheek 34 b. The moldingcavity 34 is then filled with a raw elastomer material adapted to form afilling body 33 intimately joined to the bead core 31 and thecircumferentially inextensible annular insert 32.

[0132] Preferably, filling of the mold 34 cavity is carried out byinjecting the raw elastomer material through at least one annularinjector comprising an admission opening or hollow space 35substantially extending over the whole circumferential extension of themolding cavity. In this way, a quick and homogeneous filling of themolding cavity 34 occurs, without the risk of stratification phenomenathat could arise in the elastomer material if the latter would beobliged to pass through admission channels of reduced section. It is tonote that the admission hollow space 35 may be comprised of a pluralityof slits homogeneously distributed along the whole circumferentialextension of the molding cavity 34, so as to give rise, in any case, toa quick and homogeneous filling of the molding cavity.

[0133] Accomplishment of the inextensible annular structures 4 mayadvantageously take place close to the toroidal support 11, so that saidstructures lend themselves to be picked up and laterally applied to thecarcass ply 3 by appropriate mechanical handling devices not describedas not of importance to the aims of the invention.

[0134] When application of the inextensible annular structures 4 hasbeen completed, either the carcass ply or plies, or, within the scope ofthe present invention, the side portions 23 a, 23 c, 24 a, 24 c of thedeposition sections 23, 24 are provided to have respective end flapsradially projecting towards the geometric rotation axis of the toroidalsupport 11 relative to the inextensible annular structures. These endflaps, substantially identified close to said bending regions 25, areturned back about the respective inextensible annular structures 4, asviewed from FIG. 8.

[0135] This turning-back step can be for example carried out with theaid of inflatable chambers or equivalent means associated with thetoroidal support 11. The amount by which said end flaps project andconsequently the width of the turned-back flap formed by same can beeasily established in advance by suitably adjusting the radial-movementstroke of the distributor element 22 or the radial positioning of theretention elements 26, so as to modify the width of the side portions 23a, 23 c, 24 a, 24 c in a radial direction.

[0136] Accomplishment of the carcass structure 2 can involve formationof at least one auxiliary carcass ply, not shown in the accompanyingdrawings. This auxiliary carcass ply can be directly formed insuperposed relationship upon the carcass ply 3 and the inextensibleannular structures 4, in the same manner as the primary carcass ply,optionally with deposition sections disposed in a crossed orientationrelative to the deposition sections 23, 24 forming the first carcass ply3.

[0137] In tires of the radial type, a belt structure 5 is currentlyapplied to the carcass structure 2.

[0138] Advantageously, in a novel and inventive manner, application ofthe belt structure 5 is provided to be substantially directly carriedout on the carcass structure 2 which in a preferred embodiment of theinvention can be made as previously described.

[0139] For the purpose, as diagrammatically shown in FIGS. 9 and 10,formation of at least one continuous belt ribbon 36 is provided, whichcomprises a plurality of longitudinal parallel cords 36 a, of metallicmaterial for example, at least partly incorporated into one or morelayers of raw elastomer material 36 b.

[0140] Formation of the continuous belt ribbon 36 can be achieved forexample by guiding the cords 36 a, fed from respective reels 37, througha second extruder 38, into which the elastomer material from a secondextrusion apparatus 39 flows. The continuous belt ribbon 36 emergingfrom the second extruder 38, after possible passage through firstcalendering rollers 40, is caused to pass through a cutting-off machine41 cutting it according to a given inclination α relative to itslongitudinal extension, to form belt lengths 42 the size in width ofwhich, measured perpendicularly to the cutting direction, corresponds tothe width of at least one first belt strip 6 to be obtained on thecarcass structure 2.

[0141] Lengths 42 are individually and sequentially laid down onto thecarcass structure 2 consecutively in a circumferential alignment and inmutual side by side relationship along respective junction edges 42 aparallel to cords 36 a and corresponding to the opposite longitudinaledges of the belt ribbon 36.

[0142] Therefore the assembly of lengths 42 forms the first belt strip 6of a continuous circumferential extension. As diagrammatically shown inFIG. 11, in the first belt strip 6 cords 36 a will be disposedtransversely at an inclination corresponding to the cutting inclinationof lengths 42.

[0143] Preferably this inclination has a value corresponding to 80° andin any case included between 45° and 90° relative to the circumferentialextension direction, optionally with an opposite orientation relative tothe underlying carcass ply 3.

[0144] In order that the first belt strip 6 consisting of lengths 42 ofsame extension may have a homogeneous and continuous circumferentialcourse, the continuous belt ribbon 36 emerging from the second extruder38 may be provided to have a transverse extension, measured parallellyto the cutting direction, equal to a submultiple of the circumferentialextension of the first belt strip. Alternatively, said transverseextension may be provided to be slightly lower than the value of theabove mentioned submultiple, being then suitably increased by thecalendering action carried out by rollers 40.

[0145] In conclusion, by suitably intervening on the calendering rollers40, the width of the continuous belt ribbon 36 may be adapted in such amanner that the obtained lengths 42 shall have an extensioncorresponding to a submultiple of the circumferential course of the beltstrip 6 to be made, without replacement of extruder 38 being required.

[0146] It is to point out that by the calendering operation, an increasein the distance between the individual cords 36 a is obtained,concurrently with an increase in width of the continuous belt ribbon 36,said individual cords 36 a remaining in any case spaced apart the samedistance from each other.

[0147] The above described operating sequence can be repeated in thesame manner if formation of one or more additional first belt strips,not shown in the accompanying drawings, is required, the cords of whichwould be inclined according to a crossed orientation relative to thecords 36 a of the first belt strip 6 and/or adjacent strips.

[0148] In a manner known per se, formation of the first belt strip orstrips 6 can be preceded by application of two strip-like inserts 43adapted to support the opposite side edges of the first belt strips sothat the latter may substantially keep a flat profile in transversesection.

[0149] Therefore, at least one second belt strip 7 is made, preferablyby winding of at least one continuous elongated element 44 in the formof coils disposed axially in side by side relationship and extendingcircumferentially about the first belt strip 6.

[0150] If required, the winding coils formed by the elongated element 44can be disposed side by side in a variable axial distribution pitch,which for instance is greater close to the equatorial median plane X-Xof the tire relative to the opposite side edges of the belt structure 5.

[0151] As diagrammatically shown in FIG. 12, for preparation of thecontinuous elongated element 44, one or more elementary cords 44 a fedfrom corresponding reels 45, are parallelly joined together andrubberized by passage through a third extruder 46 supplied withelastomer material from a third extrusion apparatus 47.

[0152] The elongated element 44 thus obtained has one or more elementarycords 44 a coated with an elastomer material of appropriate thicknessand is ready to be wound around the first belt strip 6, after possiblepassage through a storage device 48.

[0153] In a convenient embodiment, said cords are the well knownmetallic cords of the HE (high ultimate elongation) type, use andfeatures of which have already been widely described in the EuropeanPatent 0 461 464 in the name of the same Applicant, for example.

[0154] In more detail, these cords consist of a given number of strands,each strand being formed of a given number of individual wires of adiameter not lower than 0.10 mm and not higher than 0,40 mm, preferablyincluded between 0.12 and 0.35 mm. Wires in the strands and strands inthe cord are helically wound together in the same direction, the windingpitches for wires and strands being the same or even different.

[0155] Preferably, these cords are made of high-carbon (HT) steel wires,i.e. containing carbon to an extent not lower than 0.9%.

[0156] In a specific embodiment, particularly advantageous in the caseof tires for road haulage, said helical layer winding is preferably madeof a single cord known as 3×4×0.20 HE HT cord spiraled from one belt endto the other: said indication identifies a metallic cord formed of 3strands each consisting of four elementary wires of a diameter of 0.20mm wound in the same direction as the strands; then, as known,abbreviation HE stands for “high elongation” and abbreviation HT standsfor “high tensile”.

[0157] These cords have an ultimate elongation included between 4% and8% and a well-known typical behavior under tension, a so-called “springbehavior”.

[0158] In an alternative embodiment, specifically adopted with tires forcars, said winding is carried out with textile cords preferably of aheat-shrinkable material, such as NYLON 6 or NYLON 66 for example.

[0159] Then the tread band 8 is applied to the belt structure 5 obtainedin the above described manner.

[0160] In more detail, according to a further aspect of the presentinvention, the tread band 8 is directly formed about the belt structure5 by circumferential winding of at least one continuous sheet of rawelastomer material 49, about the belt structure in a plurality ofradially superposed coils, as diagrammatically shown in FIG. 15.

[0161] The continuous sheet of elastomer material can be advantageouslymade with the aid of a fourth extruder 50 supplied from a fourthextrusion apparatus 51. Sheet 49 emerging from the fourth extruder 50can be engaged by a further calendering unit 52, immediately downstreamof which the toroidal support 11 carrying the tire being manufacturedmay be arranged, to enable direct winding of the elastomer sheet aroundthe belt structure 5.

[0162] By appropriate cutting means associated with the calendering unit52 and/or by shutting means operating at the outlet of the fourthextruder 50 (both not shown as they can be made in any convenient mannerfor a person skilled in the art), the width of the elastomer materialsheet 49 can be advantageously progressively reduced concurrently withformation of each winding coil “S” around the belt structure 5, so thatthe elastomer sheet has a progressively decreasing width away from therotation axis of tire 1. Actually, with reference to FIG. 15, it can beeasily assumed that the radially outer coils “S” have a smaller widththan the radially innermost coils, so as to give the obtained tread band8 a desired transverse profile.

[0163] After accomplishment of the tread band 8 or optionally beforethis operating step, application of sidewalls 9 made in the mannerdiagrammatically shown in FIGS. 16 and 17, is carried out. In theembodiment shown, each sidewall 9 is made by injection of elastomermaterial into another mold 53, from which said sidewall is taken up andsubsequently laterally applied to the carcass structure 2 with the aidof mechanical handling devices or the like.

[0164] In the embodiment shown, each sidewall 9 has a radially outerportion 9 a and a radially inner portion 9 b made of different types ofelastomer material and intimately joined together by an overmoldingprocess. For the purpose, mold 53 essentially has an outer cheek 53 aand a pair of inner cheeks 53 b which are mutually interchangeable andonly one of which is shown in the drawings.

[0165] The outer cheek 53 a is first coupled with a first inner cheek(not shown) to define a first cavity within the mold, in which cavity byinjection of a first elastomer material, the radially outer portion 9 aof the sidewall 9 is formed. The inner cheek of mold 53 is then replacedby the second inner cheek 53 b such shaped that in the mold a secondcavity partly delimited by the previously-molded radially outer portion9 a is defined. This second seating is intended for receiving theradially inner portion 9 b which is formed by injection of a secondelastomer material.

[0166] Each of the sidewalls 9 formed in the above described mannerlends itself to be laterally applied to the carcass structure 2, asabove described.

[0167] Tire 1 thus manufactured is now ready to be removed from thetoroidal support 1 to be submitted to a vulcanization step that can beexecuted in any known and conventional manner.

[0168] According to a possible alternative embodiment, an air tube ofclosed tubular section may be advantageously associated with tire 1 inaddition to, or in place of liner 10, before the vulcanization step,which air tube is inserted into carcass 2 after the tire has beenremoved from the toroidal support 11. This air tube, not shown in theaccompanying drawings, will be inflated after the tire has beenintroduced into a vulcanization mold, to supply an inner pressureadapted to ensure a perfect adhesion of the tire against the mold wallsand, in particular, against the mold parts intended for defining thelongitudinal and transverse cuts 8 a of the tread pattern.

[0169] According to a further preferential feature of the presentinvention, during the vulcanization step the carcass plies 3 and beltstrips 6, 7 are submitted to a stretching step to achieve apre-tensioning thereof, giving rise to a tire expansion according to alinear extent measured on the circumferential extension at theequatorial plane X-X of the tire itself included, just as an indication,between 2% and 5%. This stretching step can be achieved by effect of theinflation pressure of the above mentioned air tube, or other type ofinflatable chamber or bladder employed in the vulcanization apparatus.

[0170] The present invention achieves important advantages.

[0171] Actually, the tire in reference can be obtained throughmanufacture of the different components directly on a toroidal supporton which the tire is gradually formed or in any case very close thereto.In this way all problems connected with manufacture, storage andmanagement of semifinished products which are common to manufacturingprocesses of the traditional type are eliminated.

[0172] It is to note in particular that formation of the carcass ply orplies by deposition of a strip-like element formed of several cordsincorporated into one elastomer layer enables important advantages to beachieved. First of all, in comparison with the method described in theabove mentioned U.S. Pat. No. 5,453,140, the manufacturing time for eachcarcass ply can be greatly reduced, due to the simultaneous depositionof as many thread-like elements as they are contained in the strip-likeelement 13. Employment of the strip-like element 13 also dispenses withthe need for previously depositing liner 10 onto the toroidal support.Actually, the elastomer layer 13 b employed in forming the strip-likeelement 13 is capable by itself to ensure an efficient adhesion ofelement 13 to the toroidal support 11, thereby ensuring a steadypositioning of the individual deposition sections 23, 24.

[0173] Positioning accuracy as regards the deposition sections and thethread-like elements integrated thereinto is further improved by thefact that the strip-like element has an important structural consistencythat makes it insensitive to vibrations or similar oscillation effectsthat can be transmitted by the deposition apparatus 28. In thisconnection it is to note that deposition of an individual thread-likeelement, as described in U.S. Pat. No. 5,453,140, makes it difficult toobtain an accurate deposition of each thread section, due exactly tovibrations and/or oscillations undergone by said thread during thedeposition step.

[0174] Furthermore, simultaneous deposition of a plurality ofthread-like elements in accordance with the invention enables thedeposition apparatus 28 to be operated at slower rates than requiredwhen deposition of the individual thread is concerned, which is afurther advantage in terms of working accuracy without on the other handimpairing productivity.

[0175] Besides, deposition of a strip-like element directly crownwise toa toroidal support of a profile substantially identical with that of thefinished tire enables densities to be achieved that cannot be reached inthe art by known methods providing deposition of a carcass ply in theform of a cylindrical sleeve and subsequent shaping of same into atoroidal form, which will consequently bring about thinning of thecarcass ply cords disposed crownwise to the finished tire.

[0176] In addition to the above, the strip-like element can be steadilyfastened to the toroidal support by a vacuum effect produced throughpossible suction ducts 28, which steady fastening by vacuum cannot beachieved by known processes carrying out deposition of an individualthread.

[0177] The inclined arrangement of side portions 23 a, 23 c, 24 a, 24 cenables expansion undergone by the tire during the stretching stepimposed to it on vulcanization to be efficiently helped. Actually,during this step, the side portions tend to take an orientation in aplane radial to the tire together with the crown portions 23 b, 24 bextending between the side portions.

[0178] Mutual superposition of the side portions close to the rotationaxis of the tire greatly strengthen the tire structure close to beads,where a greater structural strength is usually required.

[0179] Attention is also drawn to the original construction character ofthe inextensible annular structures 4 disposed at the beads. Inparticular, due to the presence of the circumferentially inextensibleannular inserts 32 combined with conventional bead cores 31, tendency ofthe bead to rotate by effect of slip thrusts is efficiently prevented.In the known art, this phenomenon led the tire to slip off therespective security hump arranged in the rim, above all when the tirewas submitted to slip thrusts under partial-deflation conditions. Byarrangement of the annular inserts 32, this drawback is eliminated andthe tire lends itself to be employed even under conditions ofpractically complete deflation without the occurrence of undesiredremoval of the bead from its seat.

[0180] Behavior of the tire bead in accordance with the presentinvention during running in slip is diagrammatically shown in FIG. 19,showing tire 1 in transverse half-section, associated with a standardmounting rim 54 which, at each of the tire beads, has a bead seat 55axially delimited by a flange 56 defining an outer side edge of the rimand a security hump 57. For the sake of clarity, section hatching hasbeen purposely omitted from tire 1 shown in FIG. 19.

[0181] As can be easily viewed from said figure, the presence of theinextensible annular insert 32 prevents the tire bead from rotatingunder the effect of the slip thrust N directed parallelly to the tireaxis, turning on its resting point against the security hump 57 arrangedin rim 54. Under this situation the slip thrust N, transmitted along thecarcass ply 3 until close to the bead rim 31, gives rise to a radialcomponent N₁ which tends to move the bead away from the bead seat 55 andis counteracted by the circumferential inextensibility of the annularstructure 4, as well as to an axial component N₂ tending to push thebead against the circumferential flange 56 ensuring maintenance of asteady positioning of same.

[0182] In this way the tire having beads made in accordance with thepresent invention lends itself to bear the so-called “J-curve Test”without removal of the bead from its seat until inflation pressures of0.5 bar, whereas in the known art tires that are unable to counteractbead displacements from their seats at pressures lower than 0.8-1.0 barare considered as acceptable.

[0183] It is also to note that annular inserts 32 supply a furtherstructure protection to the tire at the beads.

What is claimed is:
 1. A tire for vehicle wheels, comprising: a carcassstructure (2) having at least one carcass ply (3) formed of at least onethread-like element (13 a) disposed along deposition paths eachextending in a substantially U-shaped conformation about the profile intransverse section of the tire (1), and a pair of circumferentiallyinextensible annular structures each engaged close to a respectivecircumferential inner edge of the carcass ply (3); a belt structure (5)applied to the carcass structure (2) at a circumferentially externalposition thereof; a tread band (8) applied to the belt structure (5) ata circumferential external position thereof; at least one pair ofsidewalls (9) applied to the carcass structure (2) at laterally oppositepositions; wherein said at least one carcass ply (3) comprises: at leastone continuous strip-like element (13) comprising a plurality oflongitudinal and parallel thread-like elements (13 a) at least partlycoated with at least one layer of raw elastomer material (13 b); saidstrip-like element (13) having distinct deposition sections (23, 24),each of which extends in a substantially U-shaped conformation about theprofile in transverse section of the tire (1), to define two sideportions (23 a, 23 c, 24 a, 24 c) substantially extending in planesorthogonal to a geometric axis of rotation of the tire (1) at mutuallyspaced apart positions in an axial direction, and a crown portion (23 b,24 b) extending in a radially external position between the sideportions (23 a, 23 c, 24 a, 24 c); the crown portions (23 b, 24 b) ofeach deposition section (23, 24) being disposed in side by siderelationship along the circumferential extension of the tire (1),whereas the side portions (23 a, 23 c, 24 a, 24 c) of each depositionsection (23, 24) are each partly overlapped with a side portion of atleast one adjacent deposition section.
 2. The tire as claimed in claim1, wherein the side portions (23 a, 23 c, 24 a, 24 c) inmutual-overlapping relationship mutually converge at the geometric axisof rotation of the tire (1).
 3. The tire as claimed in claim 1, whereinmutual overlapping of the side portions (23 a, 23 c, 24 a, 24 c) of thedeposition sections (23, 24) progressively decreases starting from amaximum value at the radially inner ends of the side portions until azero value at transition regions between said side portions and crownportions (23 b, 24 b).
 4. The tire as claimed in claim 1, wherein theside portions (23 a, 23 c, 24 a, 24 c) in mutual-overlappingrelationship are joined to each other at a bending end region (25) wherethe strip-like element (13) is folded upon itself.
 5. The tire asclaimed in claim 1, wherein the individual deposition sections (23, 24)are laid down onto the tire (1) according to a circumferentialdistribution pitch corresponding to the width of the strip-like element(13).
 6. The tire as claimed in claim 1, wherein the individualdeposition sections (23, 24) are disposed on the tire (1) according to acircumferential distribution pitch corresponding to a multiple of thewidth of the strip-like element (13).
 7. The tire as claimed in claim 1,wherein the strip-like element (13) has a width corresponding to asubmultiple of the circumferential extension of the tire (11), asmeasured at its equatorial plane.
 8. The tire as claimed in claim 1,wherein the side portions (23 a, 23 c, 24 a, 24 c) of the depositionsections (23, 24) have regions of greater width close to the innercircumferential edges of the carcass structure (2).
 9. The tire asclaimed in claim 8, wherein the thread-like elements (13 a) comprisedwithin the strip-like element (13) are mutually moved apart at saidregions of enlarged width.
 10. The tire as claimed in claim 1, whereinsaid strip-like element (13) has a width included between 3 mm and 15 mm11. The tire as claimed in claim 1, wherein said strip-like elementcomprises three to ten thread-like elements (13 a).
 12. The tire asclaimed in claim 1, wherein each of said thread-like elements (13 a) ismade up of a textile cord of a diameter included between 0.6 mm and 1.2mm.
 13. The tire as claimed in claim 1, wherein each of said thread-likeelements (13 a) is made up of a metallic cord of a diameter includedbetween 0.3 mm and 2.1 mm.
 14. The tire as claimed in claim 1, whereinsaid thread-like elements (13 a) are disposed within the strip-likeelement (13) according to a density greater than six thread-likeelements per centimeter, circumferentially measured on the carcass ply(3) close to the median equatorial plane (X-X) of the tire (1).
 15. Thetire as claimed in claim 14, wherein said thread-like elements (13 a)are disposed within the strip-like element (13) according to a mutualdistance between centers not lower than 1.5 times the diameter of thethread-like elements themselves.
 16. The tire as claimed in claim 1,wherein said side portions (23 a, 23 c, 24 a, 24 c) have end flapsturned back about the respective inextensible annular structures (4).17. A tire for vehicle wheels, comprising: a carcass structure (2)having at least one carcass ply (3) formed of at least one thread-likeelement (13 a) disposed along deposition paths each extending in asubstantially U-shaped conformation about the profile in transversesection of the tire (1), and a pair of circumferentially inextensibleannular structures each engaged close to a respective circumferentialinner edge of the carcass ply (3); a belt structure (5) applied to thecarcass structure (2) at a circumferentially external position thereof;a tread band (8) applied to the belt structure (5) at a circumferentialexternal position thereof; at least one pair of sidewalls (9) applied tothe carcass structure (2) at laterally opposite positions; wherein eachof said inextensible annular structures (4) comprises: an annularanchoring element (31) disposed coaxially with said tire (1); acircumferentially inextensible annular insert (32) disposed axially inside by side relationship with the annular anchoring element andsubstantially extending parallelly to adjacent surfaces of the carcassply (3), said annular insert being formed of at least one thread-likeelement extending in concentric coils (32 a); a filling body (33) ofelastomer material intimately joined to the annular anchoring element(31) and the circumferentially inextensible annular insert (32).
 18. Thetire as claimed in claim 17, wherein said circumferentially inextensibleannular insert (32) is disposed axially in side by side relationshipwith the annular anchoring element (31) at a position axially externalto the latter.
 19. The tire as claimed in claim 17, wherein saidcircumferentially inextensible annular insert (32) is disposed axiallyin side by side relationship with the annular anchoring element (31) ata position axially internal to the latter.
 20. The tire as claimed inclaim 17, wherein said circumferentially inextensible annular insert(32) has a radial extension greater than the radial extension of thebead core (31).
 21. The tire as claimed in claim 20, wherein the radialextension of said circumferentially inextensible annular insert (32)substantially corresponds to at least twice the radial extension of thebead core (31).
 22. The tire as claimed in claim 1, wherein the carcassstructure (2) further comprises at least one second carcass ply similarin structure to the first carcass ply (3).
 23. A tire for vehiclewheels, comprising: a carcass structure (2) having at least one carcassply (3) formed of at least one thread-like element (13 a) disposed alongdeposition paths each extending in a substantially U-shaped conformationabout the profile in transverse section of the tire (1), and a pair ofcircumferentially inextensible annular structures each engaged close toa respective circumferential inner edge of the carcass ply (3); a beltstructure (5) applied to the carcass structure (2) at acircumferentially external position thereof; a tread band (8) applied tothe belt structure (5) at a circumferential external position thereof;at least one pair of sidewalls (9) applied to the carcass structure (2)at laterally opposite positions; wherein said belt structure (5)comprises at least one first continuous belt strip (6) formed of aplurality of belt lengths (42) each comprising at least one layer of rawelastomer material (36 b) at least partly incorporating a plurality ofparallel cords (36 a) disposed transversely, said belt lengths (42)being disposed consecutively in circumferential alignment on the tire(1) and in mutual side by side relationship along respective junctionedges parallel to said cords (36 a).
 24. The tire as claimed in claim23, wherein each of said belt lengths (42) has a circumferential sizecorresponding to a submultiple of the circumferential extension of thefirst belt strip (6).
 25. The tire as claimed in claim 23, wherein thebelt structure (5) further comprises at least one second belt strip (7)formed of at least one continuous elongated element (44) wound in coilsdisposed axially in side by side relationship and extendingcircumferentially about the first belt strip (6).
 26. The tire asclaimed in claim 25, wherein the winding coils of the continuouselongated element (44) are disposed mutually in side by siderelationship according to a varying axial-distribution pitch.
 27. Thetire as claimed in claim 26, wherein said axial-distribution pitch isgreater close to the median equatorial plane (X-X) of the tire than atthe opposite side edges of the belt structure (5).
 28. The tire asclaimed in claim 1, wherein said tread band (8) comprises at least onecontinuous sheet of raw elastomer material (49) circumferentially woundabout the belt structure (5) in a plurality of radially superposed coils(S).
 29. The tire as claimed in claim 28, wherein said continuous sheetof elastomer material (49) has a progressively decreasing width awayfrom the rotation axis of the tire (1).
 30. The tire as claimed in claim1, wherein each of said sidewalls (9) comprises a radially outer portion(a) and a radially inner portion (b) made of a first and a secondelastomer material respectively and intimately joined to each other byan overmolding process.
 31. The tire as claimed in claim 1, wherein thecarcass structure (2) is further comprised of at least one sealing layer(10) made of elastomer material impervious to air, coating said carcassply internally of the tire (1).
 32. The tire as claimed in claim 31,wherein said sealing layer or “liner” is essentially made up of at leastone ribbon-like band (12) of an air-proof elastomer material extendingin coils disposed side by side along the profile in transverse sectionof the tire (1).